Automatic camera focusing device



l Sheets-Sheet l May 2, 195@ Filed Dec. 4, 1946 TF "f M, @Avis i E f'vWW UTOMTC CMERA FOCUSING DEVICE 4 Sheets-Sheet 2 ma /Jx May 2, 1950 M.DAVIS 2,506,347

AUTOMATIC CAMERA FOCUSING DEVICE Filed Dec. 4, 1946 4 Sheets-Sheet 5ENLARGE wsuuce May 2, 1950 M, DAVls 2,566,347

AUTOMATIC CAMERA FOCUSING DEVICE Filed Dec. 4, 1946 4 Sheets-Sheet 4FII/9 7 Al' Patented May AUTMATKC CAMER FOUUSTNG DEVIEE Meyer Davis,Chicago, lll.

Application December 4, i946, Serial No. 7%,982

(Si. Bil- 2Q e Claims. l

My invention is directed to cameras, and par ticularly to processcameras of the type cornmercially employed to produce clear and accurateenlargements or reductions of an image.

Formulas for accurately determining the dis tances which must existbetween the negative, lens and the image elements of commercial processcameras to obtain satisfactory enlargements or reductions of the imageon the negative have been carefully developed and applied in theproduction oi cameras of many types. It has long been obvious that theserelationships must be maintained with the highest order of accuracy ifgood photographs are to vloe expected. Various means for mechanicallymaintaining the requisite spacing between the negative, lens and imageelements have been proposed but in general these have not been adoptedfor construction with sullicient accuracy to permit their use incoinmercial process camera work. The spacings between the elements ofprocess cameras, therefore, are usually set for each picture by skilledphotographers who calculate closely the necessary distances.

One of the irripoi'tant objects of my invention is to provide acommercial process camera, or the like, which incorporates easilyoperated focusing means for maintaining with a high order of precisionthe required spacings between the lens, negative and image elements overa wide range of settings for enlargement or reduction without requiringthe independent adjustment of the spacings between any of the elementswithin the range of the lens employed and which may therefore besatisfactorily operated by workmen of relatively limited skill.

Other important objects include the provision of such a camera in whichlenses ci" various local lengths may be interchangeably employed withonly a single initial change of spacing between the major cameraelements and in which the distances necessary for accurate focusing maybe varied by the opera-tion of a single remotely controlled motor, orthe like.

Other important objects and advantages will become apparent from thefollowing speciflcation and from the drawings in which:

Figure l is a partially sectioned side View of a camera incorporating myfocusing device;

Figure 2 is a diagrammatic top view of a camera incorporating myfocusing device;

Figure 3 is an end view of my camera;

Figure i is a partial cross section taken along the lines 5 4 ci Figurel;

lll

Figure i is a partial cross section taken along the lines 5-5 of Figurel;

Figure o is a partial cross section taken along the lines 6-6 ci Figure1;

Figure 7 is a partial cross section taken along the lines l--l oi Figurel;

Figure 8 is a partial cross section taken along f Figure 9 is a partialcross section taken along V the lines B-- of Figure l;

Figure l0 is a partial cross section taken along the lines lili9 ofFigure l;

Figure 1l is a cross section taken along the lines H--li of Figure l;

Figure i2 is a side view of the section illustrated in Figure il; and

Figure 13 is a cross section taken along the lines |3-l3 of Figure l.

lin the following specification and claims various terms have beenapplied to specific parte or sub-assemblies which for clarltyare hereindefined as follows:

copy holder relative-to the negative holder iny which the image isreproduced on the negative without enlargement or reduction, thedistance between the lens and the copy holder being equal to thedistance between the lens and the negative holder which is equal totwice the focal length of the lens employed.

Briefly, my camera includes inner and outer tracks normal to a fixednegative holder. A lead screw extends outwardly from the negative holderparallel to and substantially coextensive with the tracks and engages agear box which is moved along the tracks by the lead screw. A movablevariable screw is journaled in the goor bei: and connected by suitablegears to the lead sci-cw in such marmer that the variable screw isrotated in coordination with the constant pit-cli screw as the gear boxis moved. A copy holder, mounted Y`journaled. in the movable gear box.

on the tracks, is driven toward or away @vom negative holder by themovable variable screw nxed variable screw is journaled in a lined gearboi; which ls usually mounted on the franse ci the negative holder andis also driven by gears irons the constant pitch screw. Preferably thetwo variable pitch screws are disposed in alignment.

To enlarge the image or copy, a lens carrier, mounted for movement alongthe track, is moved to starting position and engaged to the movable gearbox by a retractable pin. The lead screw is then rotated, as by a motor,the desired degree of enlargement is obtained, which may be indicated bya dial on the med gear bos. Rota.- tion of the lead screw moves thelens, the gear box and the movable variable screw away from the negativeholder at a uniform rate, but the copy holder, which is driven by themovable variable screw, moves at the lower nonlinear rate since thethreads of the variable-screw are such that the copy holder approachesthe lens as the lens moves away from the negative holder.

If. it is desired to reduce the image, the lens' carrier and the copyholder are returned to stai-tlng position, the lens carrier disconnectedfrom the movable gear box and engaged to the xed s which the negativemay be inserted. Preferably the outer tracks 2d extend through the innervariable screw. Rotation of the lead screw,

lng during enlargenient or reduction is unnecessary.

A second set of variable screws, one carried by the movable gear box andthe other by the ied gear box, are provided and have formed on thesurface thereof variable pitch threads to which the lens carrier or the'copy holder may be engaged if desired. The pitch of these'screws iscalculated to maintain the proper space between the elements of thecamera where lenses having other focal lengths are employed. To changetherefore from a lens having a focal length of say 60 cm. to a lenshaving a focal distance or 1'1", it is necessary only, havingsubstituted the lens, to engage the pins of the copy holder and the lenscarrier with the proper thread on the variable pitch screws or in thecese orenlargement, engaging the lens holder to the constant pitchscrew. This structure, subsequently described more fully herein, hasbeen found to be highly accurate and permits the rapid production ofexcellent photographs by an operator oi rele.- tively limited skill.

As may be seen in Figures l and 2, my camera includes outer tracks Eilparallel to inner tracks 2l which are disposed at a somewhat lower leveland parallel to the optical asis ci the camera. The tracks E@ and 2i aresupported by a suitable framework including legs 22 and support niembers25 projecting upwardly from the logs at an angle to the inner tracks 2lor to the inner and outer tracks es desired. A negative holder. genorally designated 23, is supported near one end of the tracks l@ and 2lby the legs 22 and may include a frame 26 having an inner panel againstwhich a suitable light-sens1tive plate or negative is placed and anouter panel or door 2l? through panel approximately to the outer panelor door 2l to accommodate a lens carrier, generally designated 2li.

The. lens carrier 2t includes a pair of parallel members si? over theouter tracks 2t, each of which is provided with downwardly extendinglegs 3l having suitable wheels 32 which may be :danged to engage thetracks EG. It should be noted that the tracks 2t and 2l are preferablyrigid in construction, such as channel members,

.and suitably shaped to receive the wheels of the various componentparts guided in their movement by the track. The lens carrier 2S alsoincludes inner and outer spaced transverse connecting members 33 and da,respectively.

A bellows 3b is secured at one end to the frame 2d of the negativeholder 23 and at the other end to a front plate 3l which is supported bythe inner transverse connecting member 3S of the lens carrier 28. A lensplate 38 is secured to the front plate 3l and supports a suitable lens3Q. A flange extends outwarchy and downwardly from the lens plate 353and is provided with a transverse cross member d2 which rests-on theparallel members 2Q of the lens carrier. Since the length of the bellows35 may be great during enlargement; it is preferably formed in sectionswhich may be inserted or removed as needed, andV supported by a suitablerest or rests 35 mountedfor movement along the outer tracks 2d.

A copy holder, generally designated d3, includes a carrier having spacedparallel members ld to which downwardly extending legs ed are attached.Wheels All, which may be flanged, are journaled to the legs and engagethe outer tracks 2li. At least inner and outer transverse connectingmembers it and fit, respectively, are provided connecting the parallelmembers le and extending over the inner tracks 2l. A suitable board 5iis mounted on or near the outer connecting member di) and is preferablyreinforced by a bra-ce 52.

A fixed gear box 53 is secured to the frame 2li of the negative holder23 below the bellows 36. A lead screw lill having threads of constantpitch is journaled in the xed gear box 53 and extends outwardly parallelto and midway between the inner tracks 2l. The outer end of the leadscrew 5d is frictionally engaged by a ilexible coupling 5l, or othersuitable means. which is connected to the output shaft of a motor 5dsecured by a brace bil to the outer legs 22. The lead screw 56 may berotated by operation or the motor '5d or by a disengageable hand wheel59 slidably journaled in the fixed gear box 53 and provided at its innerend with teeth engaging the end or" the screw 5d.

A gear di in the gear box 53 is secured as by a key. not shown, to leadscrew 5d and engages a gear b2 which is secured to the end of an upperfixed variable screw 63 journaled in the lixed gear box EEB andextending outwardly therefrom parab lei to and immediately above thelead screw dit. A worm bfi is also secured as by a key to the lead screwand engages a worin gear ld secured to a cross shaft @l which isjournaled in the :fixed gear box A spiral gear is also secured to thecross shalt till and engages a corresponding spiral gear d@ which issecured to the end of a lower lined variable screw ll journaled in thegear box 53 and extending outwardly therefrom parallel to and below thelead screw 5d. A gear l2 is te. also secured tc the lead screw in thegear 53 and drives a jack shaft "i3 which drives a revolution countericl through bevel gears and a micrometer dial 'il by inea-ns of whichthe nurnber of revolutions or fractions thereoi performed by the leadscrew 5# from any given. position may be calculated The length of thevariable screws and il should be slightly in excess of twice the focallength of the longest focal length lens to be einployed and have formedin their surface threads of variable pitch having a face angle oi lessthan 90. The outer ends of the variable screws @t and il are journaledin a fixed support which may suitably be connected by 'transverse arrns'i9 secured to the inner tracks il i. Both the lead screw 56 and thelower variable screw il are journaled in suitable openings extendingthrough the support i3. The upper surface of the support 'i8 is providedwith a semicylindrical notch indicated at El which supports the outerend of the upper iixed variable screw S3.

A movable gear box, generally designated il?, includes a housing E3provided with shoulders @il disposed approximately midway on the housing3 which engage inner tracks 2i and is driven along the tracks 2i by asplit nut 35 secured to the housing 83 and engaging the lead screw 5ft.Bolts 88 may be employed to secure the upper half 89 ci the split nut 3Gto the lower half Qi. The housing E3 of the movable gea-r box 32 is ofsuch height that it will pass freely below the carrier oi the copyholder d3. The lead screw 54 is provided with a heyway 92 which extendsfor a substantial portion oi its length outwardly from the startingposition of the movable gear box 82. A worm S3 in the movable gear box82 is provided with a iixed key 94 slidably engaging the lreyway S2. Theworm Q3 engages a worm gear 95 which is secured to a cross shaft iiijournaied in the housing 33. A spiral gear @il secured to the crossshaft 9i operatively engages a. mating spiral gear 99 which is securedto the end of a lower movable variable screw lili journaled in thehousing 83 and extending inwardly therefrom parallel to and below thelead screw i3d.

A gear (02 also having a key engaging the keyway 92 is mounted on thelead screw Eil adjacent the worm 93 and drives a gear itil disposedwithin the housing t3. The gear iil is secured to an end of an uppermovable variable screw iiii journaled in the housing 83 and extendinginwardly therefrom parallel to and above the lead screw d. The leadscrew 5d may, for example, have a right-hand thread and the threads onboth the upper and lower fixed and movable variable screws 63, li, itiland iilcl may also be provided with right-hand threads, the pitch of thethreads on variable screw lili?, being identical with the pitch of thethreads on variable S3, and the pitch of the threads on screws lili and'ii also being identical. Therefore, it is apparent that as the leadscrew 55s is rotated, the :novable gear box 82 will be moved by thesplit nut along the tracks 2i and will also rotate the variable screws'li and t3 through gears in the xed gear box 53 and the variable screwslili and itl through gears in the movable gear box S2. The rotation oithe variable screws lili and iilil is produced while the variable screwsare being carried toward or away from the negative holder' 23 by themovable gear boi; 32. it is 0bviously unnecessary that the entire lengthof the lead screw be threaded, provided the threads and keyway 92 extendoutwardly from the starting iii; position of the movable gear i242 theend or the lead screw near the clutch The motor 5t, which engages thelead screw tlli through the exible coupling a inay be controlled bysuitable button switches mounted on the xed gear box 53. ln order toprevent overrunnlng, however, a solenoid is connected in series with themotor tit and actuates a brake lever iilil having a earn its secured toone end. The lead screw 5t is provided with a collar iii clamped to thescrew as by a bolt il?, the other end of the coupling '5l being securedto the output shaft of motor 55 by a set screw ii. A spring type lbrakeiid is pivotally supported by an arm iifi attached to a leg 22 andextends around the collar lil. The braise i it is split and providedwith ears iii which are disposed on opposite sides of the cam iii@ insuch manner that actuation of the solenoid produces rotation of the camiii@ which separates the ears lili thus releasing the brake from thecollar ii i and the lead screw 5t thereby permitting the motor SS torotate the lead screw. The motor El@ is pref erably adapted for rotationin either direction, it being obvious that as rotation in eitherdirection is stopped, the solenoid lill will be released by interruptionof the circuit to the motor, per mitting the brake iiiIv to spring intoengagement with the collar iii thus immediatelyr stopping rotation ofthe lead screw 5L?. The position o1 the screw i i2 is adapted to permitslipping of the lead. screw 5t in the collar iii ir rotation of the leadscrew is for any reason vprevented while the motor is operating.

A suitable steady rest i il is mounted on the inner. rails 2i andprovided with an opening through which the lead screw 5# extends. Thesteady rest Hl is disposed between the collar iii and the movable gearbox 82 and is provided with towing chains H8 secured to the movable gearbox and to a leg 22.

The inner connecting member i8 of the copy holder il@ is provided withan integrally formed downwardly extending tongue iid which is providedwith suitably sized vertically aligned openings iZ'i through which thelead screw lit, the upper movable variable screw 1&6, and the lowermovable variable screw lili extend. A retractable follower pin 52Eextends through a suitable opening in the tongue iis for engagement withthe upper movable variable screw iill and similar retractable followerpin iiiextends inwardly from the side of the tongue iis for engagementwith the threads on the lower movable variable screw lili'. As best seenin Figures ll and l2, the follower pins ifJZ and 23 include a stem i254extending through an opening in a boss iiii formed in the tongue iig, orother similar rneinber. A pin 52'! extends through the stern i2@ and isdisposed to support the pin i233 in raised or disengaged position byengagement with the lace or the boss 525. The boss iG, however, isprovided with a slot adapted to receive the pin ifi'i' which lowers thestem i255 a suilicient dis ance to permit the pin to engage the threadsof the screw. A spring is disposed within a counter'oore in the boss 25and engages a collar ii on the stern iii-1l. tapered point lili? extendsoutwardly from the collar ll and projects a sliori distance beyond thecounterbore when the pin i2? is in the slot 28. The iaper on the pointcorresponds to the taper or face angle of the ihre ds formed on thescrew lili and therefore en es these threads smoothly even afterconsiderable wear has occurred. The length of the counterbore issufficient to accommodate both the spring and the collar |3| which is ofsubstantial length and cooperates with the bearing between the stem |24and the boss |26 to prevent any side play or wobble in the follower.Other subsequently described follower pins are o similar structure.

Arms |33 parallel to the inner tracks 2| are secured to the movable gearbox 32 and extend inwardly therefrom below the carrier of the copyholder 43 to a point immediately below the outer transverse connectingmember 34 of the lens carrier 28 when the lens carrier and the copyholder are in starting position. Suitable connecting means such ascaptive screws |34 extend through the outer transverse member 34 intoengagement with corresponding openings formed in the arms |33. A movablesupport member |35 is fastened to the bottom of the arms |33 and hasformed therein a journal through which the lead screw 54 extends.Suitable bearings |31 are also positioned in the support member |35 inwhich the ends of the upper and lower movable variable screws |04 and|0| are journaled. The Support member |36 is provided with wheels |38engaging the inner tracks 2| on which it rides.

A steady rest |39, disposed between the xed support 18 and the movablesupport |36, includes a transverse bar |4| having wheels |fi2 engagingthe inner tracks 2|. The transverse bar |4| is provided with an opening|43 through which the lead screw 54 is journaled. Towing chains |44connect the steady rest |39 to the fixed support 18 and to the movablesupport |36 and serve to move the steady rest along the lead screw 54after the movable gear box 82 has moved outwardly a predetermineddistance.

A movable tongue |45 having aligned vertical openings through which thelead screw 54 and the upper and lower xed variable screws 63 and 1|extend is disposed below the outer transverse member 34 of the lenscarrier 28 and is provided with openings to receive captive screws |41extending through transverse member 35 thus providing means for securingthe lens carrier to the movable tongue. A retractable follower pin |43is disposed on the side of the movable tongue |45 for engagement withthe lower xed variable screw 1|. A yboss |49 extends outwardly from theouter face of the movable tongue M8 and is semi-cylindrical in shape,extending over the top of the xed support 18 when in starting position.A retractable follower pin extends through the boss |49 for engagementwith the upper xed variable screw' 63. The captive screws |41 areillustrated in Figure 13 and may include a stem |52 having an enlargedhead |53 on one end and enlarged threaded point |54 on the opposite end.A threaded opening is provided in the member 34, or other similarmembers, through which the stein 52 extends and a spring |56 isinterposed between the member 34 and the head |53 urging the screwupwardly. Thus the screw |31 is held in raised position except whenforced downwardly by hand against the pressure of the spring and engagedwith a suitably threaded opening in a member such as a boss |139.

In constructing my camera, it is necessary to consider the types oflenses which will be employed. For example, it may be desired toconstruct a camera which can interchangeably employ lenses having focallengths of 60 cm., 9, 12" and 1'7". In such case, the upper Variablescrews E3 and ||ll| are employed for movement of the 60 cm. or longestfocal length lens. Each of the lower variable screws 1| and lill areprolens and the copy holder be such as to maintain at all times thedesired spacing between the cam-Y era elements. It is, however,desirable that the gear reduction to the lower variable screws lili and1| be greater than the gear reduction to the upper variable gears IDIand 63 in order that several separate sets of threads may be formed onthe same screw. The lead screw 5d may, for example, loe provided with aright-hand thread having a pitch of 1.125" and the gear reduction to theupper variable screws |561 and 63 be 3 1, the gear reduction to thelower variable screws i|| and 1| be 48-1, and the gear reduction throughthe gear 12 in the xed gear box B3 to the dial 11 be 94-8. Once thesegear ratios have been xed in their proper relationship, it is obviousthat the proper variable pitch of the various threads employed onvariable screws 63, 1|, and mil may be accurately calculated.

Assuming that a 60 cm. lens is employed and that a photograph or otherimage has been attached to the board 5| of the copy holder 3.3 and thatit is desired to reduce the size of the copy or image on a negative inthe negative holder 23, the following sequence of operations will occur:

The lens carrier is disconnected from the arms |33 by releasing captivescrews or pins |35. Captive screws |41 are employed to attach the lenscarrier 28 to the movable tongue |46 and the follower pin |5| releasedto engage the threads on the upper fixed variable screw 63. The followerpin |53 is maintained in disengaged position and is employed only whenthe 9, 12" or 17" focal length lenses are employed. Similarly thefollower pin |23 on the tongue H3 is disengaged and the follower pin |22engaged with the threads on the upper movable variable screw |04. Thecopy holder is moved to the position indicated for the 60 cm. lens. Thelens and copy holder will then be disposed in starting position with thedistance from the center of the lens 33 to the image plane on a negativein the negative holder 23 equal to twice the focal length of the lens39. The distance from the lens 39 to the surface of the copy on theboard 5| will also be twice the focal length of the lens 39.

One of the motor control buttons l is pressed, causing the motor 58 torotate the lead screw 513 in one direction, say counterclockwise whenviewed from the negative holder. Rotation of the lead screw 55 moves themovable gear box 82 outwardly away from the negative holder along thelead screw at a linear rate and through the gears |02 and |03 producesrotation of the upper movable variable screw |04 in an oppositedirection. Since the copy holder L23 is engaged to the upper movablevariable screw Hill, it is obvious that thecopy holder 43 will also moveoutwardly but at a non-linear rate less than that of the gear box rate.The initial portion of the movement of `the copy holder d3 from startingposition with respect to the movable gear box 32 is relatively greatsince the pitch of the variable screw access? H14 is greatest at thispoint and successively becomes less as the end of the thread on thescrew IM is approached. Simultaneously with this movement, however, thelens carrier 28 is moved toward the negative at a non-linear rate sincerotation of the lead screw 54 also produces rotation of the upper xedvariable screw t3 in the opposite direction and the follower pin llconnects the lens carrier to the variable screw 63. It should be notedthat the pitch of the threads on the screw 63 is greatest near the endopposite the xed gear box 53 and that the pitch successively diminishesas it approaches the negative holder 23. The variable pitch of thescrews S3 and 104 having been properly calculated and equal, it may beseen that the image of the copy produced by the lens 39 on a negative inthe nega-tive holder 23 will at all times be in focus and that themovement may be stopped at any time by release of the button H26. It mayalso be seen that since the pitch of the threads on variable screws IMand 63 is identical, the rate of movement between the copy holder $3 andthe lens carrier 28 during reduction will be linear, but the rate ofmovement of the lens carrier 28 relative to the negative holder will benon-linear. The proper size of reduction can be determined either byviewing the image on a ground glass sheet disposed in the negativeholder for this 4- purpose or by the counter 14 and dial 'Il which canbe graduated in any convenient manner.

If it is next desired to make an enlargement of the copy on the copyholder 43, the direction of rotation of the motor 56 is reversed and thelens carrier 28 and copy holder 43 are returned to starting position.Captive screws 41 are unscrewed to release the lens carrier from themovable tongue M5 and the follower pin l5! raised to disengage thecarrier from the upper xed variable screw 63. Captive screws or pins i3dare lowered thus fastening the lens carrier 2&8 to the arms 133. Noadjustment is required for the copy holder 43.

With the parts set as described, rotation of the lead screw will drawthe lens carrier 28 outwardly with the movable gear box 82 to which itis now connected by the arms 433 and its rate of movement is thereforelinear, controlled directly by the pitch of the lead screw 5d. However,the copy holder 43, still being engaged to the upper movable variablescrew Q, approaches the lens 3S at a non-linear rate as the lens carrier28 moves outwardly, thus maintaining the desired relationship ofdistances between the copy holder 43, the lens 39, and the negativeholder 23.. Since the overall length of the lead screw 54 isconsiderable. I prefer to employ the motor 56 for most movements and amenabled to do so without diiculty due to the action of the brake H3. Itis obvious, however, that hand wheel E9 may be employed if desired.

Assuming a 60 cm. lens has been in use and it is desired to employ say a17" lens for reduction, the lens carrier is disengaged from the arms 133by pins or screws 434, secured to tongue 45 by screws lill and movedtoward the negative holder 23 until follower pin i455 engages thread Son lower xed variable screw li. The copy holder 53 is also moved bydisengaging follower pin l2? and moving the copy holder until iollowerpin V23 engages thread l59 on the lower movable variable screw lill,after which vthe operation proceeds as previously described. Forenlargement with a 17 lens, the lens carrier 28 is moved toward the copyholder 53 until pins Focal length of lens Regggton Enlargilent 60 cm1:1/5 1:6 17 inches I/Bzl/IO 3:10 l2 inches l/izl/l 4:14 il inchesl/zl/O 7:20

In the foregoing specification I have described a preferred form of mystructure in detail as required by R. S. 4888, but it is not to beunder-n stood that I wish to limit myself to the specific details hereindescribed since it is obvious that many substitutions and modificationscan be made in the described structure by those skilled in the art. Forexample, it is obviously feasible to substitute a rack for the leadscrew 54 and provide suitable gearing in the moving gear box 82 toproduce the desired operation of the parts. In such instance, means mustbe provided for translating the movement oi a pinion in the gear box 82to the nxed gear box 53 in order to produce the proper rotation ofscrews l and 63. if the camera is to be used only for enlargement, it isunnecessary, of course, to provide much of the apparatus such as thevariable screw 63 and some of the associated mechanism, since these areemployed only in making reductions. Var--y ious relationships of gearswithin the gear boxes 53 and 82 as well as the type of gears employedmay be varied without departing from the scope of my invention, as mayother of the mechanical details herein described, such as thesubstitution of rods for track. Furthermore, I may provide means forinterchanglng sets of variable screws, thus eliminating the lowervariable screws l and 10i. I do not therefore wish to limit myselfspecically to the form or my invention described herein except in so faras donned by the appended claims.

I claim:

l. In a camera having a iixed negativo holder, a lens carrier and a copyholder movable axially on track, and a constant pitch lead screw, thecombination therewith of means movable axially by said constant pitchscrew, a variable pitch screw carried by said means, means for rotatingsaid screws in fixed relation, and means for driving the copy holder bythe variable pitch screw.

2. In a camera having a nxed negative holder, a lens carrier and a copyholder movable on track, and a'constant pitch lead screw, the combination therewith of means movable axially by said screw, a variable pitchscrew carried by said means, a second variable pitch screw in axialalignment with said first mentioned variable pitch screw and rotatablymounted in xed relation relative to the 'negative holder, gears con1necting said variable pitch screws with the lead screw, means fordriving the copy holder by the first mentioned variable screw, means fordriv ingr the lens carrier by the lead screw for move ment away from thenegative holder, and mea-ns for driving the lens carrier by the secondmentioned vvariable screw for movement toward the negative holder.

3. In a camera having a xed negative holder, a lens carrier and a copyholder, the combination therewith of a constant pitch lead screw, afixed gear box, a movable gear box driven by the lead screw, a pluralityo axially aligned variable pitch screws journaled in said gear boxes,driving means connecting the variable pitch screws with the constantpitch lead screw, means for driving the copy holder by one of the pairof variable screws on the movable gear box, means for driving the lenscarrier by the constant pitch lead screw for movement in one direction,and means for driving the lens carrier by one of said variable pitchscrews journaled in the fixed gear box for movement in the otherdirection.

4. In a camera, a pair of tracks, a negative holder normal to thetracks, a rst gear box xed with respect to the tracks, a second gear boxmovable on the tracks, a constant pitch lead screw connecting the gearboxes,.a pair of variable pitch screws on each gear box, means rotatablyconnecting the variable pitch screws with the lead screw, meanssupporting the ends of the variable pitch screws, a copy holder on thetracks connectable to one of the variable pitch screws on the secondgear box, and a lens carrier on the tracks connectable to one of thevariable pitch screws on the rst gear box.

5. A focusing device for a camera having a negative holder, a movablelens carrier and a movable copy holder, comprising a constant pitch leadscrew having a keyway, a movable gear box on the lead screw,thread-engaging Vmeans on the gear box for engaging the lead screw, avariable pitch screw journaled in the gear box, a gear within the gearbox secured to the variable pitch screw, a mating gear on the lead screwhaving a key engaging said keyway, and means for operatively engagingthe copy holder with the variable pitch screw.

6. In a camera, a track, a xed negative holder normal to the track, alens carrier on the track, a copy holder on the track, said lens carrierbeing adapted to receive interchangeably a plurality of lenses havingdifierent focal lengths, a constant pitch lead screw, a movable gear boxon the tracks engaging the lead screw, a plurality f variable pitchscrews journaled on the movable gear box each having different pitchthreads, means for driving the variable pitch screws in coordinationwith the lead screw, means for engaging the copy holder with one of thevariable pitch screws when one lens is used, and means for engaging thecopy holder with another of said variable pitch screws when another lensis used.

'7. In a camera, a track, a xed negative holder normal to the track, alens carrier and a copy holder movable along the track, a constant pitchlead screw, a movable gear box on the tracks operatively engaging thelead screw, a fixed gear box, a first variable pitch screw journaled inthe movable gear box, a second variable pitch screw journaled in thefixed gear box and in axial alignment with the rst variable pitch screw,means for rotating both variable pitch screws in xed relation to thelead screw, means for engaging the copy holder to one of the variablepitch screws, and means for engaging the lens carrier to the other ofthe variable pitch screws, the pitch of the threads on each of thevariable screws being similar. v

8. In a device of the kind described, the combination of a stationarynegative holder, a movable copy holder and a movable lens positionedbetween said holder, said lens and copy holder being movable along acommon optical axis with respect to said negative holder, a movableelement, a constant pitch screw operatively connected to said element,for moving the latter in a direction away from said negative holder at apredetermined linear rate, a variable pitch screw carried by and axiallymovable with said element for moving said copy holder towards saidelement at a predetermined non-linear rate, a second like variable pitchscrew axially stationary with respect to said negative holder andadapted to be operatively connected to said lens for moving the lattertoward said negative holder at a nonlinear rate equal to the non-linearmovement of said copy holder, driving means for rotating the respectivescrews, and means for selectively operatively connecting said lensholder to either said second variable pitch screw or to said element,the relation between said screws and driving means therefore for movingsaid element, lens and copy holder being such that said negative holderis in continuous photographic focus with respect to said copy holder andlens.

MEYER DAVIS.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS France -I Oct. 4, 1937

